Centering Machine For Workpieces, Particularly Optical Lenses

ABSTRACT

A centering machine for, in particular, optical lenses has two centering spindles. The rotationally drivable centering spindle shafts are axially aligned with respect to a centering axis and constructed at the ends for the mounting of clamping bells. A stroke device axially adjusts one centering spindle shaft relative to the other centering spindle shaft along the centering axis for alignment of the lens between the clamping bells. A clamping device applies to a centering spindle shaft a clamping force clamping the aligned lens. At least one processing unit is movable relative to the centering axis, with a tool for edge processing of the clamped lens. In order to enable an optimized bell clamping process, the stroke device and the clamping device and/or a rotary drive for the axially adjustable centering spindle shaft are arranged coaxially with respect to the centering axis.

TECHNICAL FIELD

The present invention relates generally to a centering machine forworkpieces from the fields of precision optics, the horological industryand the semiconductor industry, where workpieces initially are to beclamped in centered position and subsequently processed and/or scannedat the edge. In particular, the invention relates to a centering machinefor optical lenses, in which a lens is, for edge processing thereof,clamped in a centered position, particularly in a so-called “bellclamping method” or “bell clamping process”.

PRIOR ART

Lenses for objectives or the like are centered after processing of theoptical surfaces so that the optical axis, the position of which ischaracterized by a straight line running through the two centers ofcurvature of the optical surfaces, also passes through the geometriccenter of the lens. The lens is for this purpose initially aligned andclamped between two aligned centering spindles in such a manner that thetwo centers of curvature of the lens are coincident with the common axisof rotation of the centering spindles. Subsequently, the edge of thelens is processed in a defined relationship to the optical axis of thelens, as is later necessary for installation of the lens in a frame. Inthat case, a defined geometry is imparted to the edge depending on therespective material of the lens (glass or plastic material) by machiningwith geometrically undefined or defined cutting—not only in plan view ofthe lens, i.e. circumferential profile of the lens, but also as seen inradial section, i.e. profile of the edge, for example rectilinearformation or formation with a step or steps or facet or facets.

By the above-mentioned “bell clamping process” there is to be understoodin this connection an aligning and clamping process in which the lenswith its optical axis between pot-shaped clamping bells provided at thecentering spindles is automatically aligned with respect to thevertically extending axis of rotation of the centering spindles beforeit is clamped. For this purpose, in the case of vertical arrangement ofthe centering spindles, the lens is placed on the clamping bell of thelower centering spindle, whereupon the clamping bell of the uppercentering spindle is moved in axial direction relative to the lowerclamping bell either by lowering the upper centering spindle or raisingthe lower centering spindle until the upper clamping bell also bearswith slight pressure against the lens at the contacting phase. The lensnow automatically displaces as a consequence of the curvature of theoptical surfaces thereof, optionally with addition of a suitableslip-promoting agent and/or rotation of the centering spindles, in atransverse direction, in which case the clamping bells move furthertogether for an aligning phase. The transverse movement of the lensrelative to the clamping bells as well as the axial relative movement ofthe clamping bells ends when the lens has adopted a position between theclamping bells which enables minimum spacing of the clamping bells underthe given geometric conditions. The lens, which is thus aligned by itsoptical axis relative to the axis of rotation of the centering spindles,is now firmly clamped between the clamping bells by increasing theclamping force in a clamping phase and then processed at the edge.Whereas the clamping or centering bells—often also referred to asclamping mandrels or centering mandrels are standardized for opticalmanufacturing. Incorporation by reference is expressly made with respectthereto to German Norm DIN 58736-3 of July 2001. Centering machinesadapted for this procedure are commercially known, see for example, thespecifications DE-A-37 44 118 and DE-A-100 08 710.

The centering machine disclosed in the specification DE-A-37 44 118 hastwo centering spindles, which are arranged one above the other. Thecentering spindle shafts are rotationally driven by way of belt drivesengaging at one end, are axially aligned with respect to a centeringaxis and are constructed at the mutually facing ends to each mount arespective clamping bell. In this prior art the upper centering spindleis executed as an axially fixed spindle, whereas the lower centeringspindle can be axially moved and clamped relative to the upper centeringspindle. A pressure-medium device having a plate-shaped yoke, which isarranged below the clamping spindle generates axial movements and axialforces. A diaphragm-piston/cylinder unit is arranged centrally withrespect to the clamping spindle. The unit acts on the lower end of theclamping spindle. A respective double-acting pressure cylinder with ashort-stroke piston and a long-stroke piston is attached to the unit oneither side of the centering axis. The pressure cylinders in the case ofsimultaneous pressure-loading of the short-stroke piston and long-strokepiston generate the stroke up to the point of contact of the long-strokepiston with the short-stroke piston, which is necessary in order to movethe clamping bells together up to the point of a small gap between theupper clamping bell and the lens resting on the lower clamping bell. Thediaphragm-piston/cylinder unit serves as a fine stroke device for thealigning process of the lens, by which the necessary force for alignmentof the lens is settable. The clamping force, which is required for theprocessing lens and which substantially exceeds the force generated foralignment of the lens by the diaphragm piston, is then generated solelyby the long-stroke piston after switching-off of the pressure acting onthe short-stroke piston. The diaphragm piston settles on the yoke sothat the clamping force of the long-stroke piston fully acts on theclamping spindle.

However, this prior art is capable of improvement in many respects inrelation to a bell clamping process in order to render the most optimumway possible. In the case of the provided parallel arrangement of thedouble-acting pressure cylinders there is, apart from the comparativelyhigh internal friction, also the risk of canting of the long-strokepiston due to stick-slip effects occurring to different extent frompiston to piston. Moreover, the diaphragm piston has a certain measureof intrinsic stiffness, for which reason the force needed for aligningthe lens cannot be set with very fine sensitivity. Beyond that, there isintroduction particularly when the centering spindle shafts areoptionally rotationally driven during the bell clamping process of atransverse force into the centering spindles. The transverse force canproduce a certain amount of bending and/or transverse displacement ofthe centering spindle shafts in the bearing tolerance. All this can leadto so-called “impressing” of the clamping bells on the optical surfacesof the workpieces to be clamped and other instances of surface damagethereat, which should be avoided.

A centering machine is known from DE-A-100 08 710, in which a pivotabletipping lever is provided, at one end of which the axially movablecentering spindle is pivotally connected. A compensating weight ispivotally connected at the other end of the tipping lever in order toproduce at the tipping lever a moment which counteracts the momentgenerated by the axially movable centering spindle. A combined strokeand clamping device is engaged at the same end of the tipping lever asthe compensating weight. The combined stroke and clamping device has,apart from a spring mechanism, a ball screw drive which is driven by anelectric motor and which serves the purpose of moving a centeringspindle under CNC control in axial direction relative to the othercentering spindle in order to align the workpiece between the clampingbells during contacting and aligning phases and also by way of thespring mechanism to clamp it in place during the clamping phase. In thisprior art as well, a processing unit is provided for edge processing ofthe workpiece once clamped.

This prior art mechanism, which includes a tipping lever andcompensating weight, allows a finely sensitive contacting or clampingmovement of the axially movable centering spindle in the direction ofthe workpiece, which is to be clamped, by forces which are very smalland thus able to be satisfactorily metered. However, there aredisadvantages in the respect that a certain amount of transverse forceis again introduced by way of the tipping lever into the clampingspindle, leading to a heating process in radial direction, which canoverall impair the axial alignment of the centering spindle shafts. Thesame disadvantages apply with respect to the rotary drive of thecentering spindle shafts, which here is produced by gearwheel pairsengaging at one end.

A further problem with the previously known centering machines is withthe cooling lubricant feed when edge processing of the workpiece clampedbetween the clamping bells is carried out by a grinding wheel which isrotatably mounted on a grinding spindle of the processing unit. In theprior art, the feed ends of cooling lubricant tubelets which are usedfor the cooling lubricant feed have to be positioned closely to theprocessing zone, i.e. the region of action between tool and workpiece.However, depending on the circumferential profile of the workpiece theprocessing zone migrates at the circumference of the tool so thatoptimal positioning of the cooling lubricant feed is possible withdifficulty. In addition, high circumferential speeds of the grindingwheel additionally hamper the cooling lubricant feed. In that regard,the centrifugal forces at the grinding wheel circumference and an aircushion entrained by the grinding wheel preclude sufficient wetting ofthe grinding wheel circumference. The cooling lubricant jets oriented byway of the cooling lubricant tubelets onto the grinding wheelcircumference ricochet off the grinding wheel. In order to preventgrinding burn of the workpiece, the speed of advance and/or speed ofcutting then need to be reduced, which prolongs processing time.

What is desired is a centering machine for workpieces, particularlyoptical lenses, where the problems discussed above with respect to theprior art are addressed. In particular, it is desired to have acentering machine that has an improved bell clamping process in whichso-called “impressions” and other instances of surface damage at thesensitive surfaces of the workpieces, which are to be clamped andprocessed, by the hard and sharp-edged support regions of the centeringor clamping bells are reliably avoided. In addition, it is desired thata cooling lubricant supply device provides, particularly in a centeringmachine, an improved feed of the cooling lubricant to the region ofaction between tool and workpiece.

SUMMARY OF THE INVENTION

According to a first aspect of the invention a centering machine forworkpieces, e.g. optical lenses, includes two centering spindles thatinclude respective rotationally drivable centering spindle shafts. Thespindle shafts are mounted in respective centering spindle housings andare axially aligned with respect to a centering axis. The centeringspindle shafts are constructed at mutually facing ends to each mount arespective clamping bell. A stroke device axially adjusts one of thecentering spindle shafts with respect to the other along the centeringaxis in order to align a workpiece between the clamping bells. Aclamping device can apply a clamping force to one of the centeringspindle shafts in order to clamp the workpiece aligned between theclamping bells. At least one processing unit is movable relative to thecentering axis and has a tool for edge-processing of the workpiececlamped between the clamping bells. The stroke device and the clampingdevice are arranged coaxially with respect to the centering axis.

Due to the fact that the stroke device and clamping device lie on oneand the same axis, namely the centering axis, there is no introductionby way of these devices of a transverse force during the bell-clampingprocess, namely in the clamping phase of the same, in conjunction withthe axial adjustment of the corresponding centering spindle shaft or theaxial introduction of force into the corresponding central spindleshaft. This transverse force is eliminated which otherwise could produceat the corresponding centering spindle shaft a transverse displacement,tipping moments and/or bending moments that risk the precise axialalignment of the centering spindle shafts and the circular and planarrunning thereof. Moreover, by virtue of the coaxial arrangement of thestroke device and clamping device there is no risk of derivation fromthese devices of a heating process in a direction radial with respect tothe centering axis. In the result, it is possible to reliably avoid animpermissibly large (e.g. larger than 1 to 2 microns) radial and/oraxial run-out as a consequence of axial introduction of force in theaxial adjustment of the corresponding centering spindle shaft or shaftsat the highly accurately ground clamping surfaces of the clamping orcentering bells, so that as a result undesirable impressions and otherinstances of surface damage at the workpieces, which are to be clampedand processed, cannot arise. A further advantage of the coaxiality or ofthe concentricity of the stroke device and clamping device as seen alongthe centering axis is that this arrangement is very close to thecentering axis, i.e. is a very compact construction as seen in radialdirection with respect to the centering axis, so that the at least oneprocessing unit or the tool thereof can easily reach the workpiececlamped between the clamping bells and there is no need to expend forthat purpose a greater outlay in terms of hardware.

A proprietary linear motor of synchronous, asynchronous ordouble-meshing mode of construction, optionally with stator and actuatorin lightweight construction from synthetic material parts reinforcedwith carbon fiber can be implemented for the stroke device. Preferably,the stroke device has a plunger coil drive (voice-coil actuator), whichis operatively connected with the axially adjustable centering spindleshaft and which has at least one coil coaxial with respect to thecentering axis and at least one permanent magnet co-operating with thecoil. Such a plunger coil drive, in particular, due to its coaxialrotationally symmetrical form of construction can be of very compactformat, and has only small moving mass which allows a very sensitiveregulation of the advancing force in the contacting and aligning phases.

Although the plunger coil drive can in principle be constructed with astationary magnet and moving-coil construction, a moving magnetconstruction is preferred with the permanent magnet fastened to a rotorpart connected with the axially adjustable centering spindle shaft,whereas the coil surrounding the permanent magnet is mounted in aplunger coil drive housing in fixed position in the machine. In this waycurrent supply to the plunger coil drive and cooling thereof take placein particularly simple manner. The permanent magnet can then be of veryshort construction in the axial direction, i.e. substantially shorterthan the coil, so that the advance forces of the plunger coil drive areadvantageously substantially uniform over the entire required stroke.

In further pursuance of an aspect of the invention, the clamping devicemay have an annular piston which is mounted at the axially adjustablecentering spindle shaft and forms on its side remote from the clampingbell end of the axially adjustable centering spindle shaft an annulareffective surface defining in part the centering spindle housing, aboundary of an annular chamber by way of which there can be pneumaticaction on the annular piston in order to generate the clamping force.This design makes possible, in simple manner, a satisfactory and verysensitive regulation of the clamping force during the clamping phase ofthe bell clamping process and a secure retention of the workpiece duringprocessing thereof.

In principle, the clamping spindle and fixed spindle can be arrangedthree-dimensionally as desired provided the coaxiality of the spindleshafts is ensured, for example in horizontal alignment or in verticalalignment, with an upper fixed spindle and a lower clamping spindle, asdisclosed in the specification DE-A-37 44 118. However, a design ispreferred in which the centering spindle with the axially adjustablecentering spindle shaft is arranged above the other centering spindle.In this case the annular piston forms on its side facing the clampingbell end of the axially adjustable centering spindle shaft a furtherannular effective surface defining a boundary of a further annularchamber by way of which there can be pneumatic action on the annularpiston in order to ensure pneumatic counterbalancing at the axiallyadjustable centering spindle shaft. A vertical arrangement of thecentering spindles is at the outset advantageous insofar as automaticloading of the workpiece is substantially simplified because theworkpiece placed on the lower clamping bell—by contrast with ahorizontal arrangement of the centering spindle, remains at rest there.In the case of such a vertical arrangement of the centering spindles,construction of the lower centering spindle as a fixed spindle and theupper centering spindle as a clamping spindle has in addition theadvantage, in particular, that gravitational force assists duringlowering of the clamping spindle and thus stick-slip effects, whichwould render the axial spindle movement non-uniform, are less apparentat the bearings/guides. However, for a sensitive adjustment it is thennecessary to counteract and provide compensation for the weight of theclamping spindle and the clamping bell mounted thereon, which in termsof hardware can be realized in simple manner by a pneumaticcounterbalancing. Such pneumatic counterbalancing additionally has theadvantage—by comparison with, for example, counterbalancing by acompensating weight, as disclosed in DE-A-100 08 710—that a total weightof spindle and clamping bell changing as a consequence of use ofdifferent clamping bells can be easily taken into account. In thisregard, the mentioned use of the annular piston with its annulareffective surface in a double-acting annular piston and annular cylinderarrangement is particularly advantageous, because of its coaxialposition with respect to the centering axis and the use of merely anannular piston results not only in a very compact construction,particularly in both radial and axial directions, but also equallyensures that both in application of the clamping force and inwithstanding the weight of clamping spindle and clamping bell notransverse forces are exerted on the corresponding centering spindleshaft.

In principle, the annular piston can be constructed with seals, whichwould have the advantage of low consumption of compressed air. However,an unsealed construction of the annular piston is preferred, whereby anystick-slip effects such as seal wear at the annular piston are avoided.In addition, a slight compressed air leakage over the circumferentialsurface enables finer pressure regulation by, for example, a servopressure regulating valve, with at the same time better regulatinghysteresis, since it is not necessary to firstly diminish an excessivepressure at the valve itself.

According to a second aspect of the invention a centering machine forworkpieces, e.g. optical lenses, includes two centering spindles thatinclude respective rotationally drivable centering spindle shafts. Theshafts are mounted in respective centering spindle housings and areaxially aligned with respect to a centering axis. The centering spindleshafts are constructed at mutually facing ends to each mount arespective clamping bell. A stroke device axially adjusts one of thecentering spindle shafts relative to the other one of the centeringspindle shafts along the centering axis in order to align a workpiecebetween the clamping bells. A clamping device can apply a clamping forceto one of the centering spindle shafts so as to clamp the workpiecealigned between the clamping bells. At least one processing unit ismovable relative to the centering axis and has a tool for edgeprocessing of the workpiece clamped between the clamping bells. Thecentering spindle shaft being axially adjustable by way of the strokedevice is rotationally drivable by a rotary drive which, like the strokedevice, is also arranged coaxially with respect to the centering axis.

The coaxial arrangement of the stroke device and the rotary drive forthe axially adjustable centering spindle shaft on one and the same axis,namely the centering axis produces no transverse force to thecorresponding centering spindle shaft by way of these devices during thebell clamping process when the centering spindle shafts, particularly inthe alignment phase of the bell clamping process, are optionallyrotationally driven. Neither is there an application of transverse forcein connection with axial adjustment of the corresponding centeringspindle shaft or the axial force introduction into the correspondingcentering spindle shaft nor in connection with the rotary drive of thecorresponding centering spindle shaft. Due to the centered arrangementof the rotary drive with respect to a centering axis, only a torqueabout the centering axis is generated at the corresponding centeringspindle shaft. As a consequence thereof there is no risk of a transversedisplacement or tipping and/or bending moments at the corresponding,rotationally driven centering spindle shaft, which could risk preciseaxial alignment of the centering spindle shafts and the circular andplanar running thereof. Moreover, the coaxial arrangement of strokedevice and rotary drive has no risk of a heating process, with respectto the centering axis radial direction, emanating from thesesubassemblies. As a result, undesirable impressions and other instancesof surface damage, which could arise in the case of an unacceptableradial and/or axial run-out of the clamping or centering bells due todeficient axial alignment of the rotationally driven centering spindleshafts, at the workpieces which are to be clamped and processed arereliably avoided. Moreover, the need of the arrangement concerned forconstructional space in radial direction as seen relative to thecentering axis is advantageously small, which is required for goodaccessibility of the workpiece, which is clamped between the clampingbells, during processing thereof.

In an advantageous embodiment of the centering machine the rotary drivecan be constructed as an internal rotor torque motor. A stator may bemounted in the centering spindle housing and a rotor, surrounded by thestator is attached to the outer circumference of the axially adjustablecentering spindle shaft. The rotor is longer than the stator and isaxially displaceable relative to the stator together with the axiallyadjustable centering spindle shaft. Advantages of the torque motor are,in contrast to a conventional three-phase alternating currentasynchronous motor or stepping motor, that the torque motor has onlysmall cogging i.e. stick-slipping during rotational movement, caused bymagnetic forces, and can directly exert high torques and holding momentswith high setting accuracy. Even during processing of the workpiececlamped between the clamping bells it is possible to ensure very goodsynchronous running of the centering spindle shafts or good securingagainst unintended twisting.

For axial and rotational mounting of the axially adjustable centeringspindle shaft use can be made, in principle, of slide bearings ormagnetic bearings. With respect to smallest possible bearing play,freedom from stick-slip effects and low wear with manageable cost it ispreferred if an air bearing arrangement mounts the axially adjustablecentering spindle shaft to be axially displaceable and rotatable in thecentering spindle housing. The air bearing arrangement then preferablyhas at least two air bearing sections, wherein the rotary drive isarranged axially between the air bearing sections, which ensures a highlevel of stiffness of the guide.

Advantageously, an axial run-out measuring device for checking thecentering or for checking the alignment of the workpiece after the bellclamping process can be integrated in the centering machine, by whichthe axial position of an end-face edge region of the workpiece clampedbetween the clamping bells can be detected in a direction parallel tothe centering axis. Such an economically realizable measuring device canbe provided alternatively or additionally to a laser centering device,which is known per se, and is of advantage particularly when it isnecessary to center workpieces with highly reflective or only slightlytransparent surfaces, in which circumstances laser centering devicesreach their limits.

The axial run-out measuring device preferably has a contact caliper forpositioning with respect to the end-face edge region to be scanned atthe workpiece. The contact caliper is movable together with theprocessing unit. By comparison with equally conceivable contactlesssensors, such as optical sensors, there are advantages here at theoutset in the respect that such contact calipers are robust, have a goodcost/performance ratio and operate regardless of the materialcharacteristics (for example, reflective or absorbent) of the workpiece,in which connection even slight amounts of contamination (for example,cooling lubricant droplets) on the workpiece surfaces to be scanned donot represent problems. Because the contact caliper is, in addition,movable together with the processing unit, advantageously no additionalmovement axes are required for the axial run-out measuring device.

In an advantageous embodiment the caliper of the axial run-out measuringdevice can be movable relative to the processing unit from a protectedpark position behind the tool to a measuring position protrudingrelative to the tool and conversely, so that the caliper is protectedduring the actual edge processing and there is no need to worry aboutcollision with the workpiece.

According to a third aspect of the invention, a cooling lubricant supplydevice for the supply of a cooling lubricant to a grinding wheel that isrotatably mounted on a grinding spindle of a processing unit has a feedshoe, which is mounted at least indirectly on a grinding spindle housingand seated on a circumferential surface of the grinding wheel. The feedshoe has a seating surface facing the grinding wheel. The seatingsurface has a shape substantially complementary with the circumferentialsurface of the grinding wheel and being provided centrally with apocket-like recess into which the cooling lubricant can be fed underpressure. A spring mechanism biases the feed shoe with its seatingsurface against the circumferential surface of the grinding wheel.

The feed of the cooling lubricant to the grinding wheel thus takes placeat a shape-locking gap between the circumferential surface of thegrinding wheel and the seating surface of the feed shoe, which,constructed as a shaped member, has in the region of its seating surfacea negative contour of substantially the same shape with respect to theedge contour of the grinding wheel, in particular as seen in bothtransverse section and longitudinal section. The feed shoe is pressed bythe spring mechanism in the direction of the grinding wheel. This gapsets itself automatically when the feed shoe as a consequence of feed ofthe cooling lubricant under pressure into the pocket-like recess liftsoff slightly from the grinding wheel against the spring force of thespring mechanism, in which case the gap width or gap height is dependenton the feed pressure of the cooling lubricant. The cooling lubricant isradially placed by the feed shoe on the grinding wheel and issubsequently entrained by the rapidly rotating grinding wheel bycontrast with being sprayed onto the grinding wheel.

Tests by the applicant have unexpectedly revealed that the thus-suppliedliquid cooling lubricant remains for a comparatively long time on thegrinding wheel (in part still over a grinding wheel sector of 90°)before it is spun off by the grinding wheel due to centrifugal force ascompared with the prior art outlined in the introduction. Thus, the feedshoe, which interrupts or strips off from the grinding wheel theentrained air cushion described in the introduction, can be positionedrelatively far away from the point of action between grinding wheel andworkpiece without counteracting a sufficient cooling or lubricationeffect. Resulting therefrom are not just advantages concerning workpiecehandling; in particular, migration of the point of action betweengrinding wheel and workpiece at the grinding wheel circumference whicharises specifically when the workpiece edge as seen in plan view departsfrom a circular shape does not cause any problems with respect tosufficient cooling or lubrication. The thus-produced optimum wetting andthus cooling and washing of the grinding wheel circumference furtherminimizes tool wear. Moreover, it allows high speeds of advance andcutting as well as at the same time performance of a so-called“deep-grinding method” in which tool and workpiece are in engagement notonly linearly or punctiformly, but also over a large area, which leadsto correspondingly higher levels of machining performance e.g. improvedrates of material removal.

Although centering machines are a preferred field of application or usefor the afore-described cooling lubricant supply device, the latter isof equal interest for other grinding machines in the field of optics,for example also for grinding machines with circumferential grindingwheels which serve for approximately punctiform processing of forexample aspherical lenses in rotary circumferential transverse orlongitudinal grinding methods.

In a preferred embodiment of the cooling lubricant supply device theguide shoe is made from a machinable material, preferably syntheticmaterial, wherein the seating surface of the guide shoe is ground by thegrinding wheel as a negative contour of the circumferential surface ofthe grinding wheel. An advantage results that the seating surface at thefeed shoe can thus be produced with contour precision in simple mannerand also to the extent that a grinding wheel contour changing due towear additionally transfers to the guide shoe and, in particular,automatically during processing of the workpiece.

The biasing force of the spring mechanism is preferably settable so thatthe width or height of the afore-described gap between grinding wheeland feed shoe is variable apart from the feed pressure of the coolinglubricant. In a given case, the feed pressure of the cooling lubricantcan also be kept constant by the setting of the gap. The gap is thussettable in simple manner by way of two variable magnitudes (e.g.pressure, spring force), so that wetting of the grinding wheel by thecooling lubricant can be easily optimized in correspondence with therespective use requirements.

Finally, it is preferred if the feed shoe is pivotally connected, by wayof a shoe holder, with a joint, which is fixed relative to the grindingspindle housing and which as seen in the rotational direction of thegrinding wheel lies in front of the feed shoe so that the feed shoe isplaceable substantially tangentially against the circumferential surfaceof the grinding wheel. Linear guidance of the feed shoe in radialdirection relative to the axis of rotation of the grinding wheel isindeed equally foreseeable. However, the afore-described pivotableconnection of the feed shoe is, on the other hand, advantageous to theextent that it can achieve more economical, positioning of the feed shoeat the grinding wheel. Change of the feed shoe or the grinding wheel issimpler and the risk of canting or jamming is basically no longerpresent.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail in the following by way of apreferred embodiment of a centering machine with reference to theaccompanying, partly simplified or schematic drawings. Forsimplification of the illustration, apart from parts of the cladding ofthe centering machine, the operating unit and control, discs, depositsfor workpieces and tools, the supply devices (inclusive of lines, hosesand pipes) for current, compressed air and cooling lubricant, the returnfor the cooling lubricant as well as the measuring, maintenance andsafety devices, in particular, were also mostly omitted from thedrawings, in every instance to the extent that they were not requiredfor understanding of the invention.

In the drawings:

FIG. 1 shows a perspective view of a centering machine according to theinvention for, in particular, optical lenses as workpieces, obliquelyfrom above and front right;

FIG. 2 shows a broken-away perspective view, which is enlarged in scalerelative to FIG. 1, of the centering machine according to FIG. 1,obliquely from above and laterally from the right;

FIG. 3 shows a front view of the centering machine according FIG. 1;

FIG. 4 shows a perspective view of the centering machine according toFIG. 1, obliquely from above and behind;

FIG. 5 shows a perspective view of an upper centering spindlesubassembly of the centering machine according to FIG. 1 in anillustration isolated from the rest of the centering machine, with aclamping bell which is mounted on a centering spindle shaft mounting ina centering spindle housing;

FIG. 6 shows a longitudinal sectional view of the upper centeringspindle subassembly according to FIG. 5;

FIG. 7 shows an enlarged illustration of the detail VII in FIG. 6showing, in particular, an electrical stroke device for the centeringspindle shaft, with additionally indicated compressed air supply for anair bearing arrangement for mounting a measuring head on the centeringspindle shaft;

FIG. 8 shows an enlarged illustration of the detail VIII in FIG. 6showing, in particular, an electrical rotary drive and a combinedpneumatic clamping and counterbalancing device for the centering spindleshaft, with additionally, an indicated compressed air supply for anupper air bearing section of an air bearing arrangement for mounting thecentering spindle shaft in the centering spindle housing;

FIG. 9 shows an enlarged illustration of the detail IX in FIG. 6showing, in particular, the clamping bell mounting on the centeringspindle shaft, with additionally, an indicated compressed air supply fora lower air bearing section of the air bearing arrangement for mountingthe centering spindle shaft in the centering spindle housing;

FIG. 10 shows a longitudinal sectional view of the upper centeringspindle subassembly according to FIG. 5, with an indicated power supplyfor the stroke device and compressed air supply/valve arrangement forthe combined pneumatic clamping and counterbalancing device, in a stateafter counterbalancing has been carried out in preparation for a bellclamping process;

FIG. 11 shows a longitudinal section, which is similar to FIG. 10, ofthe upper centering spindle subassembly according to FIG. 5, with aclamping bell, which after the contacting phase of the bell clampingprocess has been lowered on an optical line, during the alignment phaseof the bell clamping process;

FIG. 12 shows a longitudinal sectional view, which is similar to FIGS.10 and 11, of the upper centering spindle subassembly according to FIG.5, in a state during the clamping phase of the bell clamping process;

FIG. 13 shows a perspective view of a processing unit, which has, on theleft in FIGS. 1 and 3, a grinding spindle with a grinding wheelrotatably mounted thereon, of the centering machine according to FIG. 1in an illustration isolated from the rest of the centering machine, forillustration of a cooling lubricant supply device for the feed of acooling lubricant to the grinding wheel;

FIG. 14 shows an enlarged sectional view particularly of the coolinglubricant supply device according to FIG. 13 in correspondence with thesection line XIV-XIV shown in FIGS. 3 and 13;

FIG. 15 shows an enlarged sectional view of the cooling lubricant supplydevice according to FIG. 13 in correspondence with the section lineXV-XV shown in FIG. 14;

FIG. 16 shows an enlarged sectional view of the cooling lubricant supplydevice according to FIG. 13 in correspondence with the section lineXVI-XVI in FIG. 14; and

FIGS. 17 to 19 show perspective views of the processing unit, which ison the right in FIGS. 1 and 3, of the centering machine according toFIG. 1 in an illustration isolated from the rest of the centeringmachine without spray protection and cooling lubricant supply device forillustration of the working of an axial run-out measuring device, whichis integrated in the centering machine, for checking the centering ofthe optical lens, which is held between the clamping bells and which issimilarly schematically indicated in these figures.

DETAILED DESCRIPTION OF THE EMBODIMENT

A CNC-controlled centering machine for workpieces, particularly opticallenses L, is denoted in FIGS. 1 to 4 by 10. The centering machine 10 hasa machine bed 12 of polymer-concrete, which has a receiving space 14shown at the front in FIG. 1 for a lower centering spindle subassembly16, which is fixedly mounted on the machine bed 12. A bridge-like portalframe 18 is erected in the receiving space 14 on the machine bed 12. Theportal extends upwardly beyond the bed and carries, at a centrallocation, an upper centering spindle subassembly 20, which will bedescribed in more detail in the following with reference to FIGS. 5 to12. The lower centering spindle subassembly 16 has a lower centeringspindle 22 (referred to as a fixed spindle). The lower centering spindleshaft 24 is drivable by way of an internal runner torque motor (notshown) to rotate about a workpiece axis C1 of rotation but which isaxially fixed. The lower centering spindle 22 is mounted by air bearings(not illustrated) and is received in a lower centering spindle housing26, which in turn is fastened by a surrounding housing 28 to the machinebed 12.

As will be explained in more detail, in the first instance the uppercentering spindle subassembly 20 has an upper centering spindle 30(referred to as the clamping spindle) with an upper centering spindlehousing 32. An upper centering spindle shaft 34 is drivable to rotateabout a workpiece axis C2 of rotation and is mounted to be axiallydisplaceable. The upper centering spindle 30 engages by its centeringspindle housing 32 through a central opening in the portal frame 18,with which the centering spindle housing 32 is screw-connected frombelow by way of a mounting ring 35 (omitted in FIG. 9). The lowercentering spindle shaft 24 and the upper centering spindle shaft 34 areso arranged that they are axially aligned with respect to a verticallyextending centering axis C and are constructed at the mutually facingends to each mount a clamping bell 36, 38, as is disclosed in GermanNorm DIN 58736-3 already mentioned in the introduction. The twocentering spindle shafts 24, 34 are drivable independently of oneanother, with positional regulation in rotational angle, to rotate aboutthe workpiece axes C1, C2 of rotation; synchronous running of thecentering spindle shafts 24, 34 is achieved by CNC technology. Forplay-free and fixed mounting of the clamping bells 36, 38 each centeringspindle shaft 24, 34 is provided at the end with a conventionalhydro-expansion chuck 40, 42.

In addition, the upper centering spindle subassembly 20 according to, inparticular, FIGS. 6 to 9 includes in general—in a sequence from above tobelow as seen in the figures; respectively described in more detaillater—(i) a stroke device 44, by which the upper centering spindle shaft34 is sensitively axially adjustable relative to the lower centeringspindle shaft 24 along the centering axis C (positionally controlledclamping bell linear axis W) in order to align the optical lens Lbetween the clamping bells 36, 38, (ii) a measuring system 46 fordetecting the axial position and the angular position of the uppercentering spindle shaft 34 relative to the upper centering spindlehousing 32, (iii) a rotary drive 48, by which the upper centeringspindle shaft 34, which is axially adjustable by way of the strokedevice 44, is rotationally drivable, and (iv) a pneumatic clamping andcounterbalancing device 50 combined in the illustrated embodiment, whichserves, in particular, for application of a clamping force to the uppercentering spindle shaft 34 in order to clamp the optical lens L alignedbetween the clamping bells 36, 38. An air bearing arrangement 52 has twoair bearing sections 54, 56 for the upper centering spindle shaft 34.The rotary drive 48 and the clamping and counterbalancing device 50 lieaxially between the air bearing sections 54, 56, with the feature thatthe stroke device 44, the rotary drive 48 and the clamping andcounterbalancing device 50 are arranged coaxially with respect to thecentering axis C.

As is further evident particularly from FIGS. 1 to 4, the centeringmachine 10 comprises two processing units 58, 60, which are movablerelative to the centering axis C. Each unit 58, 60 has a respectivegrinding wheel G as a tool for edge processing of the optical lens Lclamped between the clamping bells 36, 38. The two processing units 58,60 are movable independently of one another in a work space 62. The workspace 62 is bounded laterally and upwardly by the portal frame 18. Thetwo centering spindles 22, 30 also project from below and above into thework space with the clamping bells 36, 38. Each processing unit, inparticular, can move in a direction parallel to the centering axis C(positionally controlled tool linear axis Z1 or Z2) and in a directionperpendicularly thereto (positionally controlled tool linear axis X1 orX2). The movement mechanism has for that purpose two tilted cross-tablearrangements, which are constructed and arranged in mirror symmetry withrespect to a notional plane containing the centering axis C, each with arespective driven X slide 64 or 64′ and a respective driven Z slide 66or 66′.

More specifically, two guide rails 68, 70 similarly extending parallelto one another and serving for axial guidance of the two X slides 64,64′ are mounted on the machine bed 12 behind the portal frame 18 andparallel thereto, for which purpose each X slide 64, 64′ is equippedwith two pairs of guide carriages 72, 72′, of which one pair engages oneguide rail 68 and the other pair engages the other guide rail 70. Alinear motor 76 (visible only for the X slide 64′ on the right in FIGS.1 and 2) having a respective magnet stator 78 mounted from above on themachine bed 12 and a respective coil runner 80 mounted from below on therespective X slide 64, 64′, as can be best seen in FIG. 2 is providedfor each linear drive of the X slides 64, 64′, which are guided on theguide rails 68, 70 that are provided with rubber-buffered end abutments74.

A bracket 82, 82′ at which the respective Z slide 66, 66′ is guided isscrew-connected from above on each X slide 64, 64′. For this purpose twopairs of guide carriages 84, 84′, which engage guide rails 86, 86′mounted in pairs parallel to one another on each Z slide 66, 66′, aremounted on the respective bracket 82, 82′ on the end face, which facesthe portal frame 18, in parallel arrangement. A respective servomotor88, 88′ is flange-mounted from above on the respective bracket 82, 82′and drives a threaded spindle (not shown), which engages a threaded nut(similarly not illustrated). The respective servomotor 88, 88′ providesfor the linear drive of each of the Z slides 66, 66′ . A spindle block90, 90′, on which a grinding spindle 92, 92′ of the respectiveprocessing unit 58, 60 is mounted by its grinding spindle housing 94,94′, is mounted on each Z slide 66, 66′ to face the portal frame 18.Each grinding spindle 92, 92′ conventionally includes an electric rotarydrive (not shown in more detail) for the respective grinding wheel G.

Finally, there can also be seen in FIGS. 1, 3 and 4 a spray protectiondevice 96, 96′ which is mounted on each grinding spindle housing 94, 94′and which surrounds the respective grinding wheel G up to a region ofaction for edge processing of the optical lens L. A cooling lubricantsupply device 98, 98′ is mounted on the respective grinding spindlehousing 94, 94′ by way of the spray protection device 96, 96′ and isdescribed in more detail in the following with reference to FIGS. 13 to16. In addition, parts of an axial run-out measuring device 100 forchecking the centering can additionally be seen in FIGS. 3 and 4. Themeasuring device 100 is flange-mounted at the processing unit 60 frombelow on the spindle block 90′ and is explained in more detail laterwith reference to FIGS. 17 to 19.

Further details of the above centering spindle subassembly 20 can beseen in FIGS. 5 to 9. As illustrated in FIGS. 6 and 7, the stroke device44 has a plunger coil drive 102, which is operatively connected with theaxially adjustable upper centering spindle shaft 34 and which includesone or more coils 104 coaxial with respect to the centering axis C andat least one permanent magnet 106 co-operating with the coil 104.Whereas the permanent magnet 106 is fastened to a rotor part 108, whichis fixedly connected with the axially adjustable centering spindle shaft34 by way of a screw-connection section 110 so that it can rotatetogether with the upper centering spindle shaft 34, the coil 104surrounding the permanent magnet 106 is mounted in a plunger coil drivehousing 112 which is in fixed position in the machine and which in turnsurrounds the coil 104. In FIG. 7, the substantially hollow-cylindricalplunger coil drive housing 112 is connected upwardly with a housingcover 114 fixedly screw-connected with the housing. An annular flangeplate 116 is screw-connected from below in FIG. 7 with the plunger coildrive housing 112, through which the rotor part 108 extends. The screwsare not illustrated.

The plunger coil drive housing 112 together with the coil 104, thehousing cover 114 and the flange plate 116 is supported relative to theupper centering spindle housing 32 by way of a drive holder 118, whichcan be best seen in FIG. 5. The drive holder 118 has an upper annulardisc 120 and a lower annular disc 122, which are connected together byway of two webs 124, 126 which extend parallel to the centering axis Cand are diametrically opposite one another with respect to the centeringaxis C. The plunger coil drive housing 112 extends through the upperannular disc 120 of the drive holder 118 and is fixedly connectedtherewith by way of the flange plate 116, which is flange-mounted frombelow on the upper annular disc 120 by screws (similarly notillustrated).

The measuring system 46 for detecting the axial and angular positions ofthe upper centering spindle shaft 34 is received in the free spacebetween the annular discs 120, 122 and the webs 124, 126 of the driveholder 118. As illustrated in FIG. 5, the measuring system 46 has anaxial measuring head 128, which co-operates in a manner known per sewith a measuring band 130 in order to detect the axial position of theupper centering spindle shaft 34 with respect to the centering spindlehousing 32, and an angle measuring head 132, which co-operates in amanner known per se with a measuring ring 134 (see FIGS. 6 and 7) inorder to detect the angular position of the upper centering spindleshaft 34 about the centering axis C.

Whereas the measuring band 130 is fastened to the web 124, which asshown in FIG. 5, is on the left of the drive holder 118, and almostcompletely bridges over the free space between the annular discs 120,122 of the drive holder 118, the axial measuring head 128 is mounted ona measuring head support 138 by way of a measuring head adapter 136. Theangle measuring head 132 is also fastened to the measuring head support138. The measuring ring 134, as illustrated in FIGS. 6 and 7, is mountedon a measuring ring support 140 which is connected, to be secure againstrotation, with the upper centering spindle shaft 34 at an upperprojection 142 of shaft 34.

The measuring head support 138 is mounted relative to the uppercentering spindle shaft 34 by way of a combined axial/radial air bearingarrangement 144. As illustrated in FIG. 7, the bearing arrangement hasan annular porous axial bearing pad 146 at a bearing ring 145screw-connected with the measuring head carrier 138 and a porous radialbearing bush 148 at the inner circumference of the measuring headsupport 138. As is also shown in FIG. 7, the axial bearing pad 146 andthe radial bearing bush 148 of the axial/radial air bearing arrangement144 are connected with a compressed air source Q. The axial bearing pad146 mounts the measuring head support 138 relative to the measuring ringsupport 140, and the radial bearing bush 148 mounts the measuring headsupport 138 on the upper projection 142 of the centering spindle shaft34. Finally, an air-mounted anti-twist securing device 150 rotationallysupports the measuring head support 138 at the web 126 of the driveholder 118 at the right in FIG. 5.

It is evident that the measuring head carrier 138 together with theupper centering spindle shaft 34 can move with very easy motion in axialdirection relative to the centering spindle housing 32 which is in afixed position in the machine. As a consequence of its torque supportrelative to the drive holder 118 it does not accompany and also does notobstruct the rotational movement of the centering spindle shaft 34. Tothat extent the measuring system 46 allows a very precise and sensitivedetection of the axial and angular positions of the upper centeringspindle shaft 34 with respect to the centering spindle housing 32.

As illustrated in FIGS. 5, 6 and 8, the drive holder 118 isflange-mounted by its lower annular disc 122 on an annular bearingflange 152, which in turn is screw-connected with the centering spindlehousing 32 (the screws again are not shown). The upper air bearingsection 56, which is connected with the compressed air source Q, of theair bearing arrangement 52 for the centering spindle shaft 34 isfastened in the form of a porous radial bearing bush at the innercircumference of the bearing flange 152. The lower air bearing section54 of the air bearing arrangement 52, which is similarly connected withthe compressed air source Q, is best illustrated in FIG. 9. This, too,is a porous radial bearing bush, which is mounted in a narrowed, lowersection of the centering spindle housing 32. Accordingly, the axiallyadjustable upper centering spindle shaft 34 is so mounted in thecentering spindle housing 32 by the air bearing arrangement 52 that itis axially displaceable and rotatable relative to the centering spindlehousing 32 with very easy motion. As already indicated further above,the rotary drive 48 for that and also the clamping and counterbalancingdevice 50 acting at the centering spindle shaft 34 are received incoaxial aligned arrangement between the air bearing sections 54, 56 inthe centering spindle housing 32.

The rotary drive 48 is an internal rotor torque motor, with a windingstator 154 mounted in the centering spindle housing 32 and a rotor 156.The rotor 156 is always surrounded by the stator 154 and is secured atthe outer circumference of the axially adjustable upper centeringspindle shaft 34 and which is significantly longer in axial directionthan the stator 154 and is axially displaceable relative to the stator154 together with the centering spindle shaft 34. As shown in FIG. 8,the rotor 156 has a rotor sleeve 158, which is secured on the centeringspindle shaft 34 and which in turn carries at its outer circumferencethe magnets 160 of the rotary drive 48, which are cast in place togetherwith the rotor sleeve 158 by a plastic material or synthetic resin. Therotor sleeve 158 or the magnets 160 is or are additionally fixedlysurrounded by a thin bearing sleeve 162 of the rotor 156 axially in theregion of the upper air bearing section 56 of the air bearingarrangement 52.

The clamping and counterbalancing device 50 is arranged in the centeringspindle housing 32 below the rotary drive 48. As clearly shown in FIGS.6 and 8, the clamping and counterbalancing device 50 includes an annularpiston 164 which is of unsealed construction and which is mounted at theouter circumference of the axially adjustable centering spindle shaft 45directly below the rotor 156 of the rotary drive 48. The piston 164leaves only a small annular gap (not able to be seen in the figures) toa cylinder wall 165 in the centering spindle housing 32. The annularpiston 164 forms on its side remote from the clamping bell end of theupper centering spindle shaft 34 an annular effective surface 166 whichis located in the centering spindle housing 32 adjacent to the stator154 of the rotary drive 48. The surface 166 defines, in part, an annularchamber 168 by way of which the annular piston 164 can be acted onpneumatically in order to generate the clamping force acting from belowin the figures. On its side facing the clamping bell end of the uppercentering spindle shaft 34 the annular piston 164 forms a furtherannular effective surface 170 which is larger than the effective surface166 for clamping and located in the centering spindle housing 32. Thesurface 170 defines, in part, a further annular chamber 172 by way ofwhich the annular piston 164 can be acted on pneumatically in order toensure, at the upper centering spindle shaft 34, a pneumatic weightcompensation with a force direction upwards in the figures. Thecompressed air supply for the annular chambers 168 and 172 of theclamping and counterbalancing device 50 is shown merely schematically inFIGS. 10 to 12 (compressed air source Q, servo pressure regulatingvalves V1, V2). Manometers, which are similarly schematically shown,here serve to signal which annular chamber 168 or 172 is acted onpneumatically in the bell clamping process.

FIG. 9 illustrates the clamping bell end, which is lower the uppercentering spindle shaft 34 as shown in FIG. 6. The clamping bell 38 andthe hydro-expansion chuck 42 for mounting the clamping bell 38 areconventional in nature, so that these parts do not need furtherexplanation. The hydro-expansion chuck 42 is fixedly connected with thecentering spindle shaft 34 by way of a connecting ring 174 with alabyrinth seal with respect to the centering spindle housing 32. Asshown in FIGS. 5 to 12, a passage bore 176 extends from the housingcover 114 of the plunger coil drive housing 112 to the clamping bell 38and enables, in a manner known per se, optional use of a laser centeringdevice (not shown).

The sequence of a bell clamping process shall now be briefly explainedby way of FIGS. 10 to 12, in which of the lower centering spindle or thecentering spindle shaft 24 thereof only the hydro-expansion chuck 40,which is retained thereat, with the lower clamping belt 36 is shown.

For sensitive adjustment of the clamping bell 38 by way of the uppercentering spindle shaft 34, initial compensation is to be provided forthe combined weight of the centering spindle shaft 34 together with therespective clamping bell 38 mounted thereon and all parts conjunctivelyaxially moved along the centering axis C, including the hydro-expansionchuck 42, connecting ring 174, annular piston 164 of the clamping andcounterbalancing device 50, rotor 156 of the rotary drive 48, measuringring support 140 and measuring head support 138 with the components,which are mounted thereon, of the measuring system 46, rotor part 108and permanent magnet 106 of the stroke device 44. For this purpose, theannular chamber 172 of the clamping and counterbalancing device 50 isacted on by way of the servo pressure regulating valve V2 by asensitively controlled fluid pressure which acts on the lower effectivesurface 170 of the annular piston 164 so that this lifts the mentionedcomponents. The fluid pressure when the plunger coil drive 102 isswitched off is so controlled that the centering spindle shaft 34 nolonger executes a vertical movement and is held in suspension. In thesecircumstances, the vertical movement is detected by the measuring system46 integrated in the centering spindle subassembly 20, in which case apre-selected threshold value of residual speed of the vertical movementlimits this regulating process. The fluid pressure now controlled in thelower annular chamber 172 by way of the servo pressure regulating valveV2 is kept constant for the further process. The initial state afterweight compensation has taken place is illustrated in FIG. 10.

The contacting phase of the bell clamping process can now begin, inwhich the upper clamping bell 38 is moved in direction towards the lowerclamping bell 36 in order to come into contact with the lens L placed onthe lower clamping bell. For this purpose, the plunger coil drive 102 ofthe stroke device 44 is supplied with current by way of the currentregulator S in order to lower the upper clamping bell 38 by asensitively controllable force and clearly defined travel until theupper clamping bell 38 rests on the lens L (end of contacting phase).

The centering spindle shafts 24, 34 can then be rotationally drivenabout the centering axis C, whereby the lens L easily slips intoposition, optionally with addition of a slip-promoting agent. Its tworadial surfaces then bear against the cup edges of the clamping bells36, 38. This state is illustrated in FIG. 11 and defines the end of thealignment phase.

After the lens L has thus been aligned with respect to the optical axisthereof, the plunger coil drive 102 of the stroke device 44 according toFIG. 12 is switched off again for the clamping phase of the bellclamping process. At the same time, the clamping force is increased indefined manner by pressure-loading of the upper annular chamber 168 ofthe clamping and counterbalancing device 50 and thus of the uppereffective surface 166 of the annular piston 164 by way of the servopressure regulating valve V1 to such an extent that the lens L issecurely clamped in place for the edge grinding process, which can nowtake place with the help of the processing units 58, 60.

It is evident that as a consequence of the coaxial arrangement of theactuators (stroke device 44, rotary drive 48, clamping andcounterbalancing device 50) acting on the upper centering spindle shaft34 there is no generation of transverse forces that risk the axialalignment of the centering spindle shafts 24, 34, during the bellclamping process.

The actual edge processing—in which the edge of the lens L clampedbetween the clamping bells 36, 38 is ground by the rotationally drivengrinding wheels G at the grinding spindles 92, 92′ of the processingunits 58, 60, while the grinding spindles 92, 92′ are moved, with CNCpositional regulation, in the linear axes X1, X2 and optionally Z1, Z2in correspondence with the profile to be ground at the lens L does notneed to be explained in more detail at this point, because it isfamiliar to one ordinarily skilled in the art.

As already mentioned further above with reference to FIGS. 1, 3 and 4, acooling lubricant supply device 98, 98′ for the respective grindingwheel G is provided at each processing unit 58, 60. The grinding device98 for the processing unit 58 at the left in FIG. 1 will be explained inmore detail in the following by way of FIGS. 13 to 16. The coolinglubricant supply device 98′ at the processing unit 60 on the right inFIG. 1 is constructed with mirror-symmetry with respect to the lefthandcooling lubricant supply device 98 and therefore does not need to bespecifically described.

Referring now to FIGS. 14 and 16, the cooling lubricant supply device 98generally includes a feed shoe 178, which is mounted in a mannerindirectly on the grinding spindle housing 94 and seated on acircumferential surface U of the grinding wheel G and which is made of amachinable material, preferably plastic material. The feed shoe 178 hasa seating surface 180, which faces the grinding wheel G and which has ashape substantially complementary with the circumferential surface U ofthe grinding wheel G, for which purpose the seating surface 180 ispreferably formed at the feed shoe 178 by the grinding wheel G as anegative contour of the circumferential surface U of the grinding wheelG. The feed shoe 178 is provided substantially centrally with apocket-like recess 182 into which the cooling lubricant can be fed underpressure. In addition, a spring mechanism 184 is provided to bias thefeed shoe 178 to have its seating surface 180 abut against thecircumferential surface U of the grinding wheel G, wherein in theillustrated embodiment the biasing force of the spring mechanism 184 canbe set.

According to FIGS. 13 and 14 the cooling lubricant supply device 98 ismounted on the spray protection device 96, which in turn is secured tothe grinding spindle housing 94. For this purpose, the spray protectiondevice 96 has a protrusion 186 (see FIG. 14), which carries a mount 188of the cooling lubricant supply device 98. In FIG. 14 the mount 188 isprovided on the left with a stepped passage bore 190 for reception of acontrol slide valve 192, with which, according to FIG. 15, an L push-inscrew coupling 194 for supply with the cooling lubricant is connected. Astepped transverse bore 196 opens from above in FIGS. 14 and 15 into thepassage bore 190, in which a suspension element 198 for a shoe holder200 is fastened, which in turn carries the feed shoe 178. Connectingbores 202, 204, 206, 208 in the control slide valve 192, suspensionelement 198, shoe holder 200 and feed shoe 178, respectively, ensure afluid connection between the L push-in screw coupling 194 and the recess182 in the feed shoe 178, in which case O-rings 210, 212, 214, 216provide sealing relative to the environment. The inflow quantity of thecooling lubricant can in that case be controlled by way of a controlslide valve opening 218, in that the control slide valve 192 is rotatedin the passage bore 190 of the mount 188 by way of a handle 220 at thecontrol slide valve 192.

According to, in particular, FIG. 14 the suspension element 198 isprovided at its end remote from the control slide valve 192 with a ballhead 222 which is seated in an associated seat 224 in the shoe holder200 and is secured by a setscrew 226. The ball head 222 and the seat 224thus form a joint, which lies in front of the feed shoe 178 as seen inthe rotational direction D of the grinding wheel G and is fixed relativeto the grinding spindle housing. The feed shoe 178 is pivotallyconnected by way of the substantially tubular shoe mount 200 so that thefeed shoe 178 can be placed substantially tangentially against thecircumferential surface U of the grinding wheel G. A lock 228 is mountedat the spray protection device 96 and can be removed by a handle 230 forchange of the feed shoe 178. The lock 228 forms an abutment for the feedshoe 178 in the rotational direction D of the grinding wheel G whichprevents the feed shoe 178 from being torn away from the grinding wheelG.

Further details of the spring mechanism 184 mounted in FIG. 14 on theright on the mount 188 are illustrated in FIG. 16. In the firstinstance, the spring mechanism 184 has an abutment pin 232 by way ofwhich a force can be exerted on the feed shoe 178 in direction towardsthe grinding wheel G and which engages through a stepped passage bore234 in the mount 188. A lip ring 236 is mounted in the passage bore 234,in the region of the end of the abutment pin 232 protruding beyond thefeed shoe 178 in direction towards the grinding wheel G. The lip ring236 ensures that the spring mechanism 184 is not otherwise contaminated.

The abutment pin 232 is guided in a threaded sleeve 238 to be axiallydisplaceable. A helical compression spring 240 is provided radiallybetween the abutment pin 232 and the threaded sleeve 238. The spring 240is supported not only at a step of the threaded sleeve 238, but also ata step of the abutment pin 232 so that it forcibly urges the abutmentpin 232 and the threaded sleeve 238 apart. In the operating state of thecooling lubricant supply device 98 the abutment pin 232 is, however,prevented by the feed shoe 178 from freely moving away from the threadedsleeve 238. For example, if the feed shoe 178 is removed for maintenancework, a securing ring 242 at the other end of the abutment pin 232prevents the spring mechanism from falling apart.

The threaded sleeve 238 is axially guided at the inner circumference ofthe passage bore 234 by way of an annular web. The sleeve 238 has anexternal thread 244 by which the threaded sleeve 238 is screwed into anut 246, which in turn is fixedly mounted on the mount 188. It isevident that through rotation of the threaded sleeve 238 by way of asetting wheel 248 mounted on the threaded sleeve 238 the biasing forceof the helical compression spring 240 can be set in defined manner.

In operation of the cooling lubricant supply device 98 the feed of thecooling lubricant is initially switched on so that the latter is fedunder pressure by way of the L push-in screw coupling 194, thesuspension means 198 and the shoe holder 200 to the recess 182 in thefeed shoe 178. The feed shoe 178 then functions as a hydrostatic slidebearing and slightly lifts off the circumferential surface U of thegrinding wheel G. The bearing gap of this hydrostatic bearing is, asapparent, settable by way of the bias of the helical compression spring240 in the spring mechanism 184. In testing of this cooling lubricantsupply device 98 in practice the cooling lubricant was shown to stillsurround the grinding wheel G, when rotating at high rpm, over an angleof more than 90° after leaving the storage pocket or recess 182 and onlylater at greater angles was flung away from the grinding wheel G due tocentrifugal forces. This unexpected effect makes it possible for thefeed shoe 178 to be able to be positioned relatively far away from thepoint of action between grinding wheel G and workpiece L, which in turnprovides significant advantages in (inter alia) workpiece handling. Inaddition, migration of the point of action between workpiece L andgrinding wheel G due to a non-circular outer profile of the workpiece Lno longer causes any problems in cooling or lubrication.

In a given case, for example, after the bell clamping process and beforethe actual edge processing, the centering of the lens L between theclamping bells 36, 38 can be checked by the axial run-out measuringdevice 100. As shown in FIG. 3, the measuring device 100 is integratedin the centering machine 10 and which can detect the axial position ofan end surface edge region R of the lens L, which is clamped between theclamping bells 36, 38, in a direction parallel to the centering axis C.

Details with respect thereto are subsequently illustrated with referenceto FIGS. 17 to 19, from which for this purpose the spray protectiondevice 96′ and the cooling lubricant supply device 98′ have beenomitted. The axial run-out measuring device 100 has a commerciallyavailable contact caliper 250, which extends parallel to the centeringaxis C. For positioning with respect to the end surface edge regionR—which is to be scanned—at the workpiece L, the caliper 250 is movabletogether with the processing unit 60, i.e. by the CNC axes X2, Z2, whichis illustrated in FIG. 18 by the corresponding movement arrows. Thecaliper 250 can beforehand be moved according to the correspondingmovement arrow in FIG. 17 with respect to the processing unit 60 from aprotected park position (FIG. 17) behind the grinding wheel G to ameasuring position (FIGS. 18 and 19) protruding relative to the grindingwheel G. For this purpose, a pneumatic cylinder 252 with end abutmentsis flange-mounted from below on the spindle block 90′ of the processingunit 60. A piston rod 254 selectably movable out of the pneumaticcylinder 252 in that case carries at the free end thereof a mount 256for the caliper 250. The mount 256 is in the illustrated embodiment soconstructed that it can alternatively or additionally receive a furthercaliper (not illustrated) and, in particular, in a position turnedthrough 90° relative to the caliper 250, whereby checking of the radialrun-out of the lens L clamped between the clamping bells 36, 38 wouldequally be possible. The rotational movement arrow in FIG. 19 finallyindicates that the lens L during the actual checking process, in whichthe caliper 250 contacts the end surface edge region R at the lens L, isrotated about the centering axis C.

In this fashion, a centering machine for, in particular, optical lenseshas two centering spindles. The rotationally drivable centering spindleshafts of which are axially aligned with respect to a centering axis andare constructed at the ends for mounting the clamping bells. A strokedevice is provided by which one centering spindle shaft is axiallyadjustable along the centering axis with respect to the other centeringspindle shaft for alignment of the lens between the clamping bells. Aclamping device for application of a clamping force clamps the alignedlens, to a centering spindle shaft. At least one processing unit ismovable relative to the centering axis and has a tool for edgeprocessing of the clamped lens. In order to enable an optimized bellclamping process, the stroke device and the clamping device and/or arotary drive for the axially adjustable centering spindle shaft arearranged coaxially with respect to the centering axis.

Variations and modifications are possible without departing from thescope and spirit of the present invention as defined by the appendedclaims.

1. A cooling lubricant supply device for supply of a cooling lubricant to a grinding wheel rotatably mounted as a tool on a grinding spindle of a processing unit in a grinding machine, characterized by a feed shoe, which is mounted at least indirectly on a grinding spindle housing and seated on a circumferential surface of the grinding wheel and which has a seating surface facing the grinding wheel, the seating surface having a shape substantially complementary with the circumferential surface of the grinding wheel and being provided centrally with a pocket-like recess into which the cooling lubricant can be fed under pressure, and a spring mechanism being provided, by which the feed shoe is biased with the seating surface thereof against the circumferential surface of the grinding wheel.
 2. A cooling lubricant supply device according to claim 1, characterized in that the feed shoe is made of a machinable material, preferably plastic material, and the seating surface at the feed shoe is ground by the grinding wheel as a negative profile of the circumferential surface of the grinding wheel.
 3. A cooling lubricant supply device according to claim 2, characterized in that the biasing force of the spring mechanism is settable.
 4. A cooling lubricant supply device according to claim 3, characterized in that the feed shoe is pivotally connected by way of a shoe holder with a joint, which is fixed relative to a grinding spindle housing and which lies in front of the feed shoe as seen in the rotational direction of the grinding wheel so that the feed shoe is positionable substantially tangentially against the circumferential surface of the grinding wheel.
 5. A cooling lubricant supply device according to claim 1, characterized in that the biasing force of the spring mechanism is settable.
 6. A cooling lubricant supply device according to claim 5, characterized in that the feed shoe is pivotally connected by way of a shoe holder with a joint, which is fixed relative to a grinding spindle housing and which lies in front of the feed shoe as seen in the rotational direction of the grinding wheel so that the feed shoe is positionable substantially tangentially against the circumferential surface of the grinding wheel. 